1. Field of the Invention
The present invention relates to a device and method employing lenticular retroreflective structure that can produce a flashing effect or alternately display various patterns, symbols or images in variable brightness for a spectator depending on a position of the spectator's eye relative to the device and to the location of the light source. More particularly, this invention relates to the road signs, safety markings, signaling reflectors, visual advertising displays and the like.
2. Description of Background Art
Numerous applications exist including the passive (non-illuminated) road signs, safety markings and similar devices hereinafter collectively referred to as “signs” that are made to catch the attention of the spectators, such as vehicle drivers, approaching these devices from a distance. Since a wide range of applications exist for the present invention in relation to enhancing the visibility of signs, for the sake of simplicity of expression and without limiting generality of this invention, the prior art and preferred embodiments will now be described using an example of a road sign and its visibility for the driver in an approaching vehicle.
Since the sign visibility at night is especially problematic, the signs can include various retroreflective backings, particularly in the form of a highly reflective film that enhances the sign visibility due to the efficient reflection of the light from the car headlamps back to the driver of the respective car. The conventional signs, however, are static and only capable of displaying only a single pattern or image that can be seen by the driver, and usually only in one color. While these conventional solutions improve the apparent brightness of the signs, they lack any dynamic effects such as flashing or a rapid succession of different patterns or images. Furthermore since the typical light sources, such as headlamps of a car or truck, are steady in brightness, the brightness of retroreflected light also does not change appreciably.
Active systems employing flashing light sources usually provide the sufficient brightness variability to solve the visibility problem. However, the active light sources require constant energy supply which adds to the installation and operating costs. The energy requirement is especially problematic in remote areas with no power lines and where the maintenance and energy supply can be limited. Therefore, it would be advantageous to provide the capability for the signs to display alternating brightness levels, patterns, symbols or images without the added cost and complexity of active lighting.
Static lenticular devices or screens are known that provide a view of two or more images in succession using a set of lenses or prisms arranged in an array and a specially prepared image print underlying the lens array. These prior art devices allow the eye of the spectator to see only one set of areas of the print at a time, depending on the angular orientation of the spectator's line of sight with respect to the device. In these screens, a lenticular print obtained by interlacing two or more images is attached to or printed on the back of a lenticular lens array sheet. Interlacing involves dividing the source images into stripes and combining the striped images together so that the different source images can be alternately seen by an observer depending on the viewing angle. The combination of interlaced images and a lenticular lens array produce various visual effects such as flip, animation, 3D, morph and zoom.
However, the conventional lenticular screens are usually only capable of displaying the images that are printed in the back of the lens array and their ability to catch observer's eye is usually limited to changing the image content and colors only. The image prints are scattering light into all directions thus resulting in a much poorer visibility from a distance compared to the state-of-the art signs and markings having retroreflective capabilities. Therefore, the conventional lenticuar screens are ill suited for improving the visibility of road signs or for similar sign and display applications. In many applications, including, for example, commercial advertising or road signs, it will be advantageous to enhance the visibility of the screen and its dynamic image effects, especially when the ambient illumination is inadequate.